Generation and Characterization of a TRIM21 Overexpressing Mouse Line

Specific removal of a protein is a key to understanding its function. "Trim-Away" utilizes TRIM21, an antibody receptor and ubiquitin ligase, for acute and specific reduction of proteins. When TRIM21 is expressed in cells, introduction of a specific antibody causes rapid degradation of the targeted protein; however, TRIM21 is endogenously expressed in few cell types. We have generated a mouse line using CRISPR to insert a conditional overexpression cassette of TRIM21 into the safe harbor site, Rosa26. These conditionally-expressing mice can be bred to a wide variety of Cre mice to target cell-specific TRIM21 overexpression in different tissues. Zp3^Cre mice expressed TRIM21 protein specifically in oocytes, whereas Hprt^Cre mice expressed the protein globally. When TRIM21-overexpressing oocytes were microinjected with specific antibodies targeting either the IP₃ receptor or SNAP23, these proteins were effectively degraded. In addition, cortical neural cells from globally-overexpressing TRIM21 mice showed a dramatic reduction in IP₃ receptor protein within hours after electroporation of a specific antibody. These experiments confirm the effectiveness of the Trim-Away method for protein reduction. These mice should make a valuable addition to the broader research community, as a wide range of proteins and cell types can be studied using this method.